Impact of Enriched Soil Amendments on Soil Fertility, Forage Yield, and Bioactive Compounds of Cassia angustifolia Vahl. Cultivated in Two Distinct Soil Types

The high cost of chemical fertilizers and the limited nutrient content of conventional organic sources, such as manure, compost, and charcoal, highlight the need for enriched organic amendments as an alternative. This study aimed to develop and evaluate enriched organic amendments by combining distillation waste biomass (DWB) from aromatic plants with naturally available low-grade rock phosphate (RP) and waste mica (WM). Two types of enriched products were prepared: enriched compost (ENC), produced through natural composting of DWB and blended with mineral powder, and biochar-fortified mineral (BFM), generated by hydrothermal conversion of DWB into biochar followed by mixing with mineral powder. The study assessed the effects of ENC and BFM at two application rates (2.5 and 5 t ha⁻¹) on soil properties, herbage yield, and quality of the medicinal herb Senna (Cassia angustifolia Vahl.), comparing them with conventional farmyard manure (FYM, 5 t ha⁻¹) and chemical fertilizers (CF, NPK 60-40-20 kg ha⁻¹) in two different soils under pot conditions. Both ENC and BFM enhanced soil fertility by increasing organic carbon, available nutrients, microbial biomass, and enzymatic activity. Total herbage yields increased by 21% and 16.3% with ENC and BFM, respectively, compared to FYM, while CF produced the highest dry herbage yield (32.7–37.4 g pot⁻¹) but was comparable to ENC (31.9–33.7 g pot⁻¹) and BFM (30.7–35.1 g pot⁻¹). Importantly, bioactive compound (sennoside) content in senna was significantly higher with ENC and BFM than with CF. These findings suggest that ENC and BFM not only overcome limitations of conventional FYM but also serve as cost-effective alternatives to chemical fertilizers in medicinal plant cultivation.